Hi Karin,

It is a good question, and I think it might make sense to begin by saying that a solar storm differs from our storm on Earth in that a solar storm has a magnetic structure. A solar storm is believed to be driven by some not fully understood magnetic force. The magnetic structure takes off from the solar surface under that force. When the force is strong, the magnetic strucure (often believed to be a fluxrope) can gain a very fast speed that causes an intense solar storm. The fluxrope does expand when it gets further out from the Sun, but it doesn't totally break apart, and their shape may change but still keep the general structure in the space, and carries the magnetic field, mass, and energetic particles with it to the Earth in a few days, and also goes beyond Earth.

Yan